added stem python library

lib/stem/prereq.py

@@ -0,0 +1,131 @@
+# Copyright 2012-2013, Damian Johnson and The Tor Project
+# See LICENSE for licensing information
+
+"""
+Checks for stem dependencies. We require python 2.6 or greater (including the
+3.x series). Other requirements for complete functionality are...
+
+* pycrypto module
+
+  * validating descriptor signature integrity
+
+::
+
+  check_requirements - checks for minimum requirements for running stem
+
+  is_python_27 - checks if python 2.7 or later is available
+  is_python_3 - checks if python 3.0 or later is available
+
+  is_crypto_available - checks if the pycrypto module is available
+"""
+
+import inspect
+import sys
+
+try:
+  # added in python 3.2
+  from functools import lru_cache
+except ImportError:
+  from stem.util.lru_cache import lru_cache
+
+CRYPTO_UNAVAILABLE = "Unable to import the pycrypto module. Because of this we'll be unable to verify descriptor signature integrity. You can get pycrypto from: https://www.dlitz.net/software/pycrypto/"
+
+
+def check_requirements():
+  """
+  Checks that we meet the minimum requirements to run stem. If we don't then
+  this raises an ImportError with the issue.
+
+  :raises: ImportError with the problem if we don't meet stem's requirements
+  """
+
+  major_version, minor_version = sys.version_info[0:2]
+
+  if major_version < 2 or (major_version == 2 and minor_version < 6):
+    raise ImportError("stem requires python version 2.6 or greater")
+
+
+def is_python_27():
+  """
+  Checks if we're running python 2.7 or above (including the 3.x series).
+
+  :returns: **True** if we meet this requirement and **False** otherwise
+  """
+
+  major_version, minor_version = sys.version_info[0:2]
+
+  return major_version > 2 or (major_version == 2 and minor_version >= 7)
+
+
+def is_python_3():
+  """
+  Checks if we're in the 3.0 - 3.x range.
+
+  :returns: **True** if we meet this requirement and **False** otherwise
+  """
+
+  return sys.version_info[0] == 3
+
+
+@lru_cache()
+def is_crypto_available():
+  """
+  Checks if the pycrypto functions we use are available. This is used for
+  verifying relay descriptor signatures.
+
+  :returns: **True** if we can use pycrypto and **False** otherwise
+  """
+
+  from stem.util import log
+
+  try:
+    from Crypto.PublicKey import RSA
+    from Crypto.Util import asn1
+    from Crypto.Util.number import long_to_bytes
+    return True
+  except ImportError:
+    log.log_once("stem.prereq.is_crypto_available", log.INFO, CRYPTO_UNAVAILABLE)
+    return False
+
+
+@lru_cache()
+def is_mock_available():
+  """
+  Checks if the mock module is available. In python 3.3 and up it is a builtin
+  unittest module, but before this it needed to be `installed separately
+  <https://pypi.python.org/pypi/mock/>`_. Imports should be as follows....
+
+  ::
+
+    try:
+      # added in python 3.3
+      from unittest.mock import Mock
+    except ImportError:
+      from mock import Mock
+
+  :returns: **True** if the mock module is available and **False** otherwise
+  """
+
+  try:
+    # checks for python 3.3 version
+    import unittest.mock
+    return True
+  except ImportError:
+    pass
+
+  try:
+    import mock
+
+    # check for mock's patch.dict() which was introduced in version 0.7.0
+
+    if not hasattr(mock.patch, 'dict'):
+      raise ImportError()
+
+    # check for mock's new_callable argument for patch() which was introduced in version 0.8.0
+
+    if not 'new_callable' in inspect.getargspec(mock.patch).args:
+      raise ImportError()
+
+    return True
+  except ImportError:
+    return False